Photovoltaic (PV) systems are ubiquitous contributors to worldwide energy production. Solar panels within PV systems convert incident sunlight into electrical energy that may be fed through an inverter to a utility power grid, stored in battery banks or locally consumed. The solar panels have a long specified operating life and are typically installed on rooftops and other sites that may be difficult to access during the operating life. Accordingly, it is desirable to monitor the performance of the solar panels to detect degradation due to aging, faults, or environmental conditions, because even minor degradation in performance of one or more solar panels can deprive the PV system of significant energy production over the long operating life of the solar panels.
Inverters within PV systems that are coupled to the utility power grid, or “grid-tied”, typically have capability to monitor the total operating voltage and total operating current cumulatively provided by all of the solar panels within the PV system. While this monitoring capability provides a useful performance measure for the entire PV system, it does not enable detection of subtle degradations within the solar panels.
Electrical characteristics, such as current-voltage, or “I-V”, characteristics, of the solar panels are definitive indicators of the performance and integrity of the solar panels, and may be used to detect even subtle degradations of the solar panels. The I-V characteristics of individual solar panels may be measured using traditional curve tracers in manufacturing facilities, prior to integration into a PV system. These measurements, disclosed for example by Warner et al. in U.S. Pat. No. 4,456,880, titled I-V Curve Tracer Employing Parametric Sampling, provide a baseline performance measure for the individual solar panels in the manufacturing environment, but do not provide for on-going monitoring of the solar panels once the solar panels are installed and are operating in a PV system.
The I-V characteristics of one or more solar panels may also be measured upon installation of the solar panels in a PV system to provide a cumulative baseline performance measure for all of the solar panels in the operating environment of the installation site. However, this measurement typically relies on disconnecting the solar panels from the rest of the PV system and disrupting operation of the PV system, which makes this type of measurement too intrusive for monitoring performance and detecting degradation of the solar panels within an installed PV system.
In view of the above, there is a need for a solar monitor that measures electrical characteristics of solar panels during the operating life of an installed PV system, without significantly disrupting the operation of the PV system.